The typical operation of a continuous jet printer may be described as follows. Electrically conducting ink held under pressure in a pressurized chamber of a print head escapes from a calibrated nozzle, thus forming an ink jet. Under the action of a periodic stimulation device, the ink jet thus formed is interrupted at a single point in space at regular time intervals. This forced fragmentation of the ink jet is usually induced at a point called the breaking point of the jet by periodic vibrations of a piezoelectric crystal placed in the ink contained in the pressurized chamber on the upstream side of the nozzle. Starting from the break point, the continuous jet is transformed into a stream of identical ink drops at a regular spacing. A first group of electrodes called “charge electrodes” is placed close to the break point, the function of which is to selectively transfer a predetermined quantity of electrical charge, for each drop in the stream of drops. All drops in the jet then pass through a second arrangement of electrodes called the “deflection electrodes” forming an electrical field that will modify the path of the charged drops.
In a first variant embodiment of so-called continuous deviated inkjet printers, the quantity of charge transferred to the drops in the jet is variable and each drop is deflected by an amount proportional to the electrical charge that was previously assigned to it. The point on the print support at which a drop lands depends on this electrical charge. Non-deflected drops are recovered by a gutter forming part of the print head and are recycled towards an ink circuit.
One known embodiment of a continuous deviated jet printer is illustrated in FIG. 1.
A printer comprises a reservoir 111 containing electrically conducting ink 110 that is distributed through a distribution channel 113 to a drops generator 116. The drops generator 116 forms an ink jet from the pressurized ink contained in the distribution channel 113, and breaks this jet into a stream of drops. These drops are selectively electrically charged using a charge electrode 120 powered by a voltage generator 121. The charged drops pass through a space between two deviation electrodes 102, 103. Their deviation varies depending on their charge. The least deviated drops, and undeviated drops, are directed towards an ink recovery container or a gutter 106, while other deviated drops are directed towards a substrate 127 locally supported by a support 213. The successive drops in a burst reaching the substrate 127 can thus be diverted to a low extreme position, a high extreme position and successive intermediate positions. All drops in the burst form a line with width Δx perpendicular to a direction Y in which there is a relative forward movement of the print head and the substrate. The print head is formed by means 116 for generating the ink jet and separating it into drops, the charge electrode 120, the deviation electrodes 102, 103, and the gutter 106. This head is usually enclosed in a casing not shown. The time elapsed between the first and the last drop of a burst is very short. The result is that despite a continuous movement between the print head and the substrate, it may be considered that the substrate has not moved with respect to the print head during the time of a burst. The bursts are fired at regular intervals in space. The combination of the relative movement of the head and the substrate, and the selection of drops in each burst that are directed towards the substrate, provides a means of printing any pattern like that shown as 128 in FIG. 1.
In order to perform its function, it is clear that the print head of a printer must be connected hydraulically firstly to a pressurized reservoir, and secondly to a receptacle receiving back ink not directed to the substrate. In general, in addition to the ink supply and recovery connections, the print head comprises connections to an ink solvent reservoir and a compressed air inlet. Electrically, the head must be connected to voltage supply sources, signal sources, so as to receive voltages and information necessary for the electrical power supply for the drop formation means, for example a piezoelectric crystal, and charge and deviation electrodes. It should be noted that voltage necessary for the deviation electrodes may be of the order of several thousand volts. With such values, the electrical connection must be particularly well insulated.
For these purposes, a print head of a printer is provided with one or several electrical fittings and one or several hydraulic fittings. Each of these electrical and hydraulic fittings has to be connected during assembly or replacement of a print head.
It has been explained in patent application EP 0 805 035 A2 that the connection of an umbilical transporting data, fluids and the electrical power supply to the print head, has always been a complicated process involving welding with high precision machines when the umbilical is welded, or deformations and twisting of cables when the umbilical is screwed. It is practically impossible to disassemble the umbilical without causing damage.
Patent application EP 0 805 035 A2 describes a system shown in the figure of this EP application, for connecting an umbilical 1 and a structure 2 to support a print head that will simplify assembly and disassembly of the umbilical. A rigid cap 3 housing the print head is located between the support structure 2 of the print head and the umbilical 1. A threaded terminal part 7 of the umbilical may easily be screwed/unscrewed in a threaded opening 9 of the cap 3. When this is done, the cap 3 fitted with the umbilical is fitted onto the support 2 using the screws 5. A locknut 8 installed on the thread 7 between the umbilical and the cap 3 locks the assembly.